Microchip Capillary Electrophoresis-Electrochemistry with Rigid Graphite-Epoxy Composite Detector

Abstract

A new rigid graphite-epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end-column wall-jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal-to-noise ratio when compared to glassy carbon detector. The performance of rigid graphite-epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis-rigid graphite-epoxy composite detector were optimized. [5,6]. Particularly, conducting composites are materials that were widely utilized for electrochemical detection of organic compounds in flowing liquids (i.e., FIA, HPLC) [7,8]. The composite electrodes act as arrays of microelectrodes, they show the response comparable to the conventional electrodes but with low noise level [9]. So far, there were published only two reports on use of carbon paste composite electrodes for detection in microfluidic systems [5,6]. However, there is no report on the use of the rigid carbon composites, which have favorable mechanical stability properties compared to carbon pastes [10] in microchip electrophoresis-electrochemistry (mCE-EC). In this work, we, for the first time, describe and characterize the use of the rigid graphite-epoxy composite-based detectors for microchip system. The new rigid graphite-epoxy composite (GEC) electrode was fabricated in plastic sleeve and aligned opposite to the microchip outlet [11] and its performance was carefully characterized. Figure 1 compares the noise level under electrophoretic conditions (applied separation voltage of þ 1500 V, detection potential þ 0.7 V) of rigid GEC electrode and of glassy carbon (GC) electrode. It can be observed that the use of the GC electrode ( Figure 1A, a) results in higher noise (about 23 pA) levels than the rigid GEC electrode ( Figure 1A, b) (noise about 11 pA) even though that GC electrode has smaller geometric surface area (7.1 mm 2 for GC vs. 9.6 mm 2 for GEC) [12]. Figure 1B depicts the dependence of the background noise upon the detection voltage. The background noise of the GC electrode (a) is around 19 pA in the range of 0 to þ 0.6 Vand then increases, reaching 183 pA at potential þ 1.0 V. The background noise of the rigid GEC electrode increases slowly from 0 to þ 0.7 V from 8.7 to 11 pA and therefore increases more rapidly, reaching level of 32 pA at potential þ 1.0 V. Such a low background noise of rigid GEC electrode is related to the microarray behavior of composite electrodes [9,10,12]. Figure 2 shows hydrodynamic voltammograms for the oxidation of dopamine (A) and catechol (B) using GC (a) and GEC (b) electrodes. The curves were recorded pointwise by making 100 mV changes in the applied potential over 0 to þ 1.0 V range. Both compounds (dopamine and catechol) display similar sigmoidal voltammetric profiles on both electrodes, with the no response in interval from 0 to þ 0.2 V, than fast rise up to þ 0.6 V (dopamine) and þ ...

Carbon nanotube detectors for microchip CE: Comparative study of single‐wall and multiwall carbon nanotube, and graphite powder films on glassy carbon, gold, and platinum electrode surfaces

“…A variety of carbon electrodes were used, i.e., thick-film screen-printed electrodes [23][24][25], carbon fibers [26], carbon paste [27], or graphite-epoxy composite electrodes [28] were employed as electrochemical (EC) detector for microfabricated chip electrophoresis. Coupling of the CNT film electrochemical detectors with microfluidic systems was demonstrated recently for analysis of purines, chlorophenols, hydrazines, amino acids (using a single-wall CNT (SWCNT) film deposited on carbon thick-film screen-printed electrode) [29], aminophenols (using a SWCNT film deposited on gold electrode) [30], and carbohydrates (using a multiwall CNT (MWCNT)/copper composite electrode) [31].…”

Microchip electrophoresis with wall‐jet electrochemical detector: Influence of detection potential upon resolution of solutes

“…(i) There are very often used detection potentials lower than the potential on current HDV plateau are often used due to more favorable S/N ratio in mCE-EC wall-jet configuration [13,14,20] (we also observed increase in background noise at detection potentials above 10.7 V). While the use of relatively low detection potential can bring advantages in terms of more favorable S/N level, it decreases resolution of the analytes, and it should be borne in mind when optimizing analytical assays in mCE-EC wall-jet systems.…”

“…Wall-jet configuration using sensing macroelectrodes is very widely employed in mCE systems for the simplicity of electrode fabrication (screen-printing [13][14][15][16][17][18][19], rigid graphite-epoxy packing [20], or the use of commercial disk electrodes [21][22][23][24][25][26]) and electrode alignment. The wall-jet macroelectrode is easily exchangeable, allowing fast and convenient replacement if passivated or allowing the use of different electrode materials.…”

Nanomaterials as electrochemical detectors in microfluidics and CE: Fundamentals, designs, and applications

“…This design has a significant advantage over CNT-film detectors because composites are mechanically stable and significantly reducing noise levels. This is a typical characteristic of composite electrodes, which can act as an array of micro/nanoelectrodes with heavily overlapping diffusion zones [36], thereby providing signals equivalent to macroelectrodes but with reduced noise and a high S/N ratio [49]. See Fig.…”